U.S. patent number RE28,767 [Application Number 05/588,185] was granted by the patent office on 1976-04-13 for drawing table.
This patent grant is currently assigned to Franz Kuhlmann KG. Invention is credited to Arnold Gundlach, Franz Kuhlmann, Horst Seiffert.
United States Patent |
RE28,767 |
Kuhlmann , et al. |
April 13, 1976 |
Drawing table
Abstract
A drawing table having a stand and a board linked to the stand
in such a manner as to allow the board to be adjusted in position
whereby the weight of the board creates a second moment about the
axis opposing the first moment. A compensating means varies the
second moment to compensate for variations in the first moment due
to changes in the position of the board so that the board is
balanced in any position.
Inventors: |
Kuhlmann; Franz (Wilhelmshaven,
DT), Gundlach; Arnold (Wilhelmshaven, DT),
Seiffert; Horst (Wilhelmshaven, DT) |
Assignee: |
Franz Kuhlmann KG
(Wilhelmshaven, DT)
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Family
ID: |
27183772 |
Appl.
No.: |
05/588,185 |
Filed: |
June 19, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
296586 |
Oct 11, 1972 |
03826204 |
Jul 30, 1974 |
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Foreign Application Priority Data
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Oct 11, 1971 [DT] |
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2150633 |
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Current U.S.
Class: |
108/2; 108/4 |
Current CPC
Class: |
A47B
27/06 (20130101) |
Current International
Class: |
A47B
27/06 (20060101); A47B 27/00 (20060101); A47F
005/12 () |
Field of
Search: |
;108/1-10 ;248/372 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Frazier; Roy D.
Assistant Examiner: Lyddane; William E.
Attorney, Agent or Firm: Holman & Stern
Claims
We claim:
1. A drawing table including a stand, a board, a horizontal spindle
constituting an axis rotatably mounted in the stand, a first arm
mounted on the spindle adjacent each end thereof, a second arm
pivotally mounted on the spindle adjacent each end thereof, each of
said first arms being pivotally attached to said board, a link arm
pivotally attached to each of said second arms and to said board, a
compensating member having a peripheral spiral groove rotatably
mounted adjacent each end of said spindle, a cable having first and
second ends, said cable being attached at the first end to the
compensating member and located in the spiral groove, a
counterbalancing means adjustably connected to the stand, and the
second end of the cable being attached to the counterbalancing
means, the attachment of the cable to the compensating member in
the spiral groove enabling the point of action of the
counterbalancing means to vary with respect to the pivot axis
during rotation of the compensating member with respect to the
pivot axis, the arrangement being such that the first and second
arms and the link arms connecting the board to the horizontal
spindle allow the board to be adjusted in position and in which the
weight of the board creates a first moment about the axis and the
counterbalancing means creates a second moment about the axis, with
said compensating member varying the second moment to compensate
for variations in the first moment due to changes in the position
of the board whereby the board is balanced in any position
thereof.
2. The drawing table as claimed in claim 1 in which the
counterbalancing means is a helical spring.
3. The drawing table as claimed in claim 2 in which the adjustable
connection of the counterbalancing means to the stand includes an
eyebolt to which the helical spring is attached, a bracket on the
stand receiving the eyebolt, and an adjustment nut for the eyebolt
for adjusting the position of the eyebolt on the bracket for
varying the tension of the helical spring.
4. The drawing table of claim 1 further comprising a receiving disc
fixed to said first arm and rotatable about said axis, the
receiving disc being linked to the compensating member having a
peripheral spiral groove for varying said point of application.
5. The drawing table of claim 4 wherein the compensating member is
a partial disc sector.
6. The drawing table of claim 5 wherein the compensating member has
a pivotably secured screwbolt carrying a thrust element which is
adjustable by means of a nut on the screwbolt and rotatably secured
in a transversely directed recess of the receiving disc.
7. The drawing table of claim 6 wherein the compensating member has
a recess situated in the sides of the spiral helical groove of the
corrector member and extending transversely to the spiral helical
groove adjacent the screwbolt, a securing element for the cable of
the helical spring being rotatably secured in said recess.
8. The drawing table of claim 7 wherein the link arm is connected
to an adjustable lever acted upon by a second spring which is
secured on a spring mounting of the stand, the spring mounting
being adjustable in vertical and horizontal directions.
9. The drawing table of claim 8 wherein the helical spring, cable,
and compensating member are housed within the stand.
10. The drawing table of claim 9 wherein the drawing board is
displaceably arranged on a securing bar which is pivotably fixed to
said first arm and said link arm.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a drawing table comprising a stand
and a drawing board which is secured by means of linkage means,
pivotably journalled on the stand head, with the weight of the
drawing board being counter-balanced in any position of the
board.
PRIOR ART
Drawing tables are known, in which the weight balancing action is
performed by springs or "gas" springs. With such drawing tables,
the weight of the drawing board inclusive of accessories such as a
drafting machine, receptacle, etc., is determined precisely, and
the spring or springs are selected accordingly. It is observed in
practice however that the characteristic curves of the springs or
"gas" springs incur differences which do not allow uniform weight
balancing. A difference may arise moreover in the weight of the
drawing boards, of the drafting mechanism and/or other accessories,
which may be counteracted only be means of springs having a
different rating. The operation of hooking and unhooking the
springs is very difficult and onerous and can be performed by a
trained operative only. In addition, the springs incur fatigue in
the course of time, the characteristic curve of a spring changes
and weight balancing is thus inoperative. For this reason, the
joints and brake of the drawing tables have been given a stiff
action, so that a balance may be established by means of the
additional friction.
OBJECT AND SUMMARY OF THE INVENTION
The present invention is intended to eliminate these shortcomings.
It attempts to provide so precise a weight or counter balance, to
provide an adaptation to change conditions of the drawing board
effective weight, in such an uncomplicated way that the drawing
table joints may be arranged to pivot freely.
According to the present invention, there is a drawing table
comprising a stand, a board, linkage means pivotably connecting the
board to an axis on the stand in a manner allowing the board to be
adjusted in position and whereby the weight of the board creates a
fist moment about said axis, counterbalancing means creating a
second moment about said axis opposing the first moment and means
for varying the second moment to compensate for variations in the
first moment due to changes in position of the board so that the
board is balanced in any position thereof.
Preferably, the means for varying the second moment comprises means
for varying the point of application relative to said axis of a
force creating the second moment.
Furthermore, the linkage means comprises a first arm pivotably
attached to said axis on the stand and pivotably attached to the
board, thereby linking the stand to the board; a second arm
pivotably attached to said axis on the stand; and a link arm
pivotably attached to the board and said second arm.
Also the counterbalancing means may be a helical spring attached at
one end to the stand and at another end to a correct member
rotatable about said axis upon movement of the board.
The point of action of the spring is adjustable or displaceable.
Due to this displaceability, it is possible to take up tolerances
in a simple manner and to allow so precise an adjustment that the
bearing points of the parallelogram linkage means, in particular
the bearing in the stand head, may be equipped with needle roller
or ball bearings, so that the drawing table may be moved without
effort in the unbraked state. This table may accordingly also be
used by female drafting personnel while working in the seated
position.
A complementary adjustment means is provided according to the
present invention, by the fact that the free extremity of the
balancing helical spring is hooked to an eyebolt which is
adjustably arranged on the stand for varying the tension of the
balancing spring. In conjunction with the possibility of displacing
the point of action, which results in a change of the moment
applied by means of the spring, adjustments may be made within wide
limits, so that the inclusion of complementary accessories on the
drawing board may also be considered without impairing the free
displaceability of the drawing table in the unbraked state.
A preferred embodiment of the invention is characterized in that a
pivot spindle to which the first or upper rocking arm is firmly
connected, has fastened thereto a disc-shaped receiving element for
a corrector disc rotatable around the axis of the pivot spindle, of
which the outer rim extends spirally and has a receiving groove for
a cable connected to the balance spring. The lever arm with which
the balancing spring acts with respect to the pivot spindle axis is
varied by turning the corrector disc with respect to the receiving
element due to the spiral form of the corrector disc. The opposing
moment engendered by the helical spring is varied thereby.
The corrector disc is concomitantly and preferably constructed as a
partial disc and comprises a swivellably secured screwbolt carrying
a thrust element adjustable by means of a nut, and held in a
rotatable manner in a transversely directed recess of the receiving
element. The displacement of the corrector disc with respect to the
receiving element is thus performed by turning the nut on the
screwbolt, a sticking or jamming action during the displacement
being prevented by virtue of the rotatable arrangement of the
thrust element in the recess of the receiving element.
To secure the cable fastened to the balancing spring in non-jamming
manner and according to a further embodiment of the invention, the
corrector disc has a recess arranged transversely to the receiving
groove at the extremity of the latter on its extremity bearing the
screwbolt, with a securing element for the cable of the balancing
spring being held rotatably in said recess. The securing element
concomitantly extends transversely to the disc and bears against a
collet situated on the extremity of the cable.
Due to the spirally shaped form of the periphery of the corrector
disc, which is coupled to the pivot spindle through the receiving
element and is thus entrained in rotation in case of a pivotal
displacement of the rocking arm during the displacement of the
drawing board, the moment applied by the spring with respect to the
pivot spindle axis undergoes an adaptation to the position of the
drawing board changed with respect to the pivot spindle axis. A
precise weight balancing action is thus assured in all positions of
the board.
According to a further embodiment of the invention, the
parallelogram link may be connected to an adjustable lever which is
acted upon by at least one other spring which has its other
extremity secured to a spring mounting which is displaceable in the
vertical and horizontal direction. This spring equally serves the
purpose of balancing, and the adjustment may be made either on the
lever or the spring mounting. This adjustment serves the purpose of
adaptation to the different tilted positions of the drawing
board.
In further development of the invention, the weight balancing
system is situated within the stand which is hollow. Accordingly,
no linkage projects behind the stand, and a considerable saving of
space is accomplished thereby.
To permit equilization between the different center of gravity
positions resulting from the incorporation of a carriage drafting
mechanism in place of a parallelogram drafting mechanism, and
according to a further embodiment of the invention, the drawing
board is arranged to be displaceable with respect to a securing or
supporting bar acted upon by the pivoting linkage arms. In
conjunction with the already defined balancing system, this
arrangement renders it possible to employ carriage drafting
mechanisms as well as parallelogram drafting mechanisms on the
drawing table, without having to perform a replacement of the
springs of the balancing system.
A particular embodiment will now be described, by way of example,
with reference to the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially sectioned front view of a drawing table
without a board,
FIG. 2 is a section along the line II--II of FIG. 1, the view
looking in the direction of the arrows, and
FIG. 3 is a section along the line III--III of FIG. 1, the view
looking in the direction of the arrows.
DETAILED DESCRIPTION OF THE DRAWINGS
A pivot spindle 2 constructed as a hollow spindle is arranged in
freely rotatable manner by means of needle roller bearings 3 in the
upper portion of a stand or pedestal 1 consisting of two pedestal
feet. Upper pivot or rocking arms 4 are firmly coupled to the pivot
spindle 2, for example by being cast integral therewith.
The pivot spindle 2 has a continuous tube 6, a partial tube 5a
extending within a brake situated on the stand or pedestal head in
each case, and a covering tube 5b situated between the brakes. The
tubes 5a and 5b are firmly joined to the continuous tube 6 by means
of a rivet 7.
Only the arrangement on the left-hand side pedestal column 1 is
described in the following, since the right-hand side column is
symmetrical and identical thereto. A receiving element 8 is
fastened by means of a grub screw 9 to extremity 6a of the tube 6.
Between the upper pivot arm 4 and the needle roller bearing 3 is
situated another rocking arm 10 which is firmly joined to a bearing
tube 10a by integral casting, with the bearing tube 10a being
pivotably arranged within the braking system and rotatable on the
tube 6. The arms 4 and 10 comprise entraining pins 4a for braking
plates 11 and 12 of the braking system. Between the two rocking
arms 4 and 10 are situated plate springs 13 which bear directly
onto the tube 6 and have the purpose of separating the braking
plates 11 and 12 from each other when the brake is released.
Accordingly, the plate springs 13 bear against the partial tube 5a
connected to the rocking arm 4 and against the bearing tube 10a
connected to the rocking arm 10. A bolt 14 which secures
intermediate braking plates 11a and 12b is firmly inserted into a
pedestal head 1a.
A parallelogram link arm 15 is pivotably journalled on the rocking
arm 10 and is joint-coupled to a securing bar 17. The bearing bolts
employed for the articulation joints are marked 19. A drawing board
18 is fastened to the securing bar 17 on which the upper rocking
arm 4 is jointedly secured by means of bearing bolts 19 and
together with the rocking arm 10 and the parallelogram link arm 15
forms a movable parallelogram. Fastening is performed by means of
screws 20 passing through longitudinal slots 17a of the securing
bar 17 and thus allowing for the displacement of the drawing board
18 with respect to the securing bar. This displacement of the
drawing board in the slots of the securing bar is required for
adjustment of the weight balancing action by displacement of the
center of gravity, which remains to be described in detail.
The parallelogram link 15 is connected to a lever 16 which is
displaceable with respect to the arm 15. The lever 16 is acted upon
by two springs 21 whose other extremities are hooked into a spring
suspension system 22 which is held on the pedestal head 1a in
vertically as well as horizontally displaceable manner. Together
with another spring whose incorporation remains to be described the
springs 21 serve the purpose of weight balancing.
The receiving element 8 has a groove 8a extending concentrically to
the pivot axis of the pivot spindle 2 and receiving a corrector
disc 23 which engages with an appropriate projection 23a in the
groove 8a. The corrector disc 23 is constructed as a partial disc
in the form of an annular sector and at it extremity which is that
situated at the top in the assembled state, has a screwbolt 25
which is jointedly fastened on the corrector disc 23 by means of a
fork element 25a and a bolt 26. The screwbolt 25 traverses a thrust
element 24 which is borne in a recess 8b of the receiving element
8. A nut 27 which bears on the thrust element 24 is operated on the
screwbolt 25 to adjust the corrector disc 23 with respect to the
receiving element 8.
As apparent from FIGS. 1 and 3, the corrector disc 23 is equipped
with a reception groove 23a for a cable 29 which is connected to a
tension spring 32. The cable 29 is immobilized on the upper
extremity of the corrector disc by means of a cylindrical securing
element 28, with the securing element 28 concomitantly being held
rotatably in a corresponding recess 23b extending transversely to
the receiving groove 23a. The securing element 28 then bears on a
collet 31 joined firmly to the cable 29. A suspension loop in which
is hooked the balance spring 32, is formed by means of a clamping
sleeve 30 at the other extremity of the cable.
The other extremity of the balancing spring 32 is hooked into an
eyebolt 33 which is inserted into a bracket 34 of the pedestal 1
and secured by means of a nut 35 employed to adjust the tension of
the spring 36 marks a sealing flap giving access to the adjusting
nut 35 within the hollow pedestal 1, wherein the balancing springs
are housed.
The external edge of the corrector disc 23, meaning the bottom of
the reception groove 23a, is spirally formed so that the point of
action of the balancing spring 32 varies with respect to the pivot
axis during rotation of the corrector disc with respect to the
pivot axis.
The table weight balancing operation is performed by fine
adjustment throughout the course of the displacement, by means of
the corrector disc 23. The tension of the balancing spring 32 is
varied by means of the nut 35, if additional equipment is installed
in the system. The tilting movement applied through the
parallelogram link 15 and the lever 16 is performed by displacement
of the lever 16, or at the bracket 34. Since this displacement has
a secondary importance in the balancing action, the springs 21
normally do not require adjustment. The optional incorporation of a
carriage or parallelogram drafting mechanism on the drawing board
may be taken into account by displacement of the drawing board 18
in the longitudinal slots 17a of the securing bar 17 and by varying
the spring tension of the balancing spring 32, so that the
compensation system may be employed for carriage as well as
parallelogram drafting mechanisms, without conversion.
* * * * *